Experience with Cape Seals on heavily trafficked roads leading to improved design and larger aggregate utilisation

Cape Seals have been used as a surfacing since the early 1960's on new construction and rehabilitation projects. It requires low maintenance and is especially economical to construct in rural environments when compared to the alternative of hot mix asphalt. It has been used extensively on the national routes in South Africa which have seen a steady increase in the heavy vehicle traffic volumes. As a result of the heavy traffic and high surface temperatures, designers have been forced over time to cut back the binder application rates to minimise the occurrence of flushing of the tack coat. The design binder content has been reduced to such an extent that less than the practical minimum binder applications are being called for using the current aggregate sizes. Hot, cold and polymer modified binders have been used as a tack coat along with pre-coated and uncoated stone as well as the merits of using different gradings for the crusher sand in the slurry. This paper describes the research and development of innovations that make the conventional Cape Seal more durable and the work that has been carried out leading up to the design and construction of a large aggregate Cape Seal which can tolerate high traffic volumes and temperatures.